Many industries make use of pre-tensioned fasteners when securing components together. In the oil and gas industry, for example, pre-tensioned bolt or stud connectors may be used to connect sections of pipe via bolted flange connections, split sleeve clamp axial flanges or the like.
In order to maintain the coupling between the mating faces of the components to be coupled, the tensile force applied to the bolts is typically selected to be in excess of the expected separation force acting on the mating faces in use, this tensile force pre-tensioning the coupling.
One method of applying pre-tension to a bolt involves the use of a stud tensioner, whereby a hydraulic cylinder is used to stretch the stud to induce the required tensile force in the stud. A nut may then be located on the stretched stud and, in use, the nut maintains the strain when the hydraulic load is removed, thereby pre-tensioning the stud.
In an alternative method, a nut may be located on a stud and a manual or hydraulic torque wrench used to apply a predetermined torque to the nut to provide the required pre-tension.
However, the insertion and manipulation of bolts can be challenging and requires bulky specialist equipment and, in particular where access space is limited, this can be awkward and time consuming.
Furthermore, as bolts require external access, these cannot be used inside sealed compartments. A result of this is that pressure sealed couplings which are restrained by bolts are typically restrained on the opposite side of the coupling to the separation force, this resulting in a large unbalanced load on the coupling.